Bending mandrel



5, 1961 R. I. GILL 2,996,101

BENDING MANDREL Filed Nov. 28, 1958 2 511 9 11 1; 1

INVENTO'R Ron/F114) kwuvs GLL Aug. 96 R. l. GILL 2,996,101

BENDING MANDREL .Filed Nov. 28, 1958 2 Sheets-Sheet 2 Patented Aug. 15,1961 2,996,101 BENDING MANDREL Ronald 'Irwine Gill, Harrow, England,assignor to The General Electric Company Limited, Kingsway, London,England Filed Nov. 28, 1958, Ser. No. 776,854 Claims priority,application Great Britain Dec. 2, 1957 Claims. (Cl. 153-63) The presentinvention relates to waveguides and methods of bending waveguides.

It has been suggested that waveguides formed, for example, ofrectangular aluminum or brass tubing may be bent, while maintaining theinternal dimensions of the original waveguide, by substantially fillingthe waveguide, prior to bending, with a mandrel comprising a number offlat strips of metal such as spring steel which are riveted together atone end. The waveguide is then bent on a suitable machine with themandrel in place. It has been found however that there is a tendency,with this arrangement, for the outer strips of metal to break.

One object of the present invention is to provide a method of bendingwaveguides in which this undesirable tendency is reduced.

According to the present invention a method of bending a waveguidecomprises the Steps of: substantially filling the waveguide, at leastover that length of the waveguide which is to be bent, with a mandrel,said mandrel comprising a stack of substantially flat metal stripshaving, at least over that part of their length which lies within thelength of the waveguide which is to be bent, a width slightly less thanthe dimension of the internal crosssection of the wave guide parallel towhich the said strips are arranged to lie, while the said stack ofstrips includes a first group of strips which are clamped or otherwiseattached together at a point beyond one end of the waveguide and asecond group of strips which are clamped or otherwise attached togetherat a point beyond the opposite end of the waveguide, and all the stripsof said second group lie between two adjacent strips of said first groupat least over that length of the waveguide which is to be bent; bendingthe said waveguide; and removing the said mandrel.

The said strips may be formed of a resilient metal such as steel.

Preferably said first and second groups are each formed by a stack ofstrips which has been doubled back on itself, to double the effectivethickness of the original stack, and then clamped at a point adjacentthe loop so formed.

Two methods of bending a waveguide in accordance with the presentinvention will now be described by way of example with referecene to theaccompanying drawings in which:

FIGURE 1 shows a perspective view of a mandrel being loaded into awaveguide,

FIGURE 2 shows a partly cut-away side elevation of an arrangement usedin the first method of bending a waveguide, and

FIGURE 3 shows a plan view of an arrangement used in the second methodof bending a waveguide.

In both the methods to be described the waveguide which it is requiredto bend is a length of waveguide formed of cartridge brass, that is tosay an alloy of copper containing approximately 30% of zinc, having aninternal cross-section of approximately 0.4 inch by 0.9 inch.

Prior to bending, the waveguide is cut to a length of say ten inches,care being taken to ensure that the plane of the cut at each end of thewaveguide is at right angles to the longitudinal axis of the waveguide.The waveguide is deburred and a small hole is drilled near one end forease of handling during the subsequent heat treatments.

As the material of the waveguide is normally too brittle to besatisfactorily cold worked it is annealed in an air circulating furnace.The furnace is brought to a temperature of 600 C. and a number ofwaveguides then loaded in. The waveguides are hung vertically, from thesmall hole previously mentioned, to minimise bowing at the elevatedtemperature. The temperature of the furnace is maintained steady at 600C. for fifteen minutes and the waveguides are then quickly removed andquenched in water, this being followed by a dip in an acid bath to remove scale.

Referring now to FIGURE 1 of the drawings, a mandrel is then drawn intoone of the lengths of waveguide 1. This mandrel is made up of aplurality of flat strips of spring steel, the strips havingsubstantially uniform crosssections along their lengths. The width ofthe strips is some two to four thousandths of an inch less than thedimension of the internal cross-section of the waveguide 1 which is atright angles to a wall of the waveguide 1, the plane of which is to bethe same both before and after the waveguide has been bent. The totalthickness of the strips making up the mandrel is some one to twothousandths of an inch less than the other dimension of the internalcross-section of the waveguide 1.

The strips forming the mandrel are made up of one single strip 2 and twogroups of strips 3 and 4. These two groups 3 and 4 are similar, and eachgroup 3 or 4 comprises a number of strips formed into a stack which isthen doubled back on itself and held with a clamp 5 or 6 respectivelynear the point where it has been bent. The group of strips 3 or 4 thushas a loop 7 or 8 respectively formed at one end and this loop 7 or 8 isarranged to be around part of the circumference of a bobbin 9 or 10respectively, which has a rectangular channel -11 or 12 respectivelyaround its circumference. The group of strips 3 or 4 lies within thischannel 11 or 12 and the clamps 5 and 6 are drawn up close to therespective bobbin 9 or 10 so that it is not able to fall out during thesubsequent operations.

The mandrel and the waveguide 1 are lubricated With tallow and themandrel is then loaded into the waveguide 1 as follows. The group ofstrips 3 is loaded first and pushed through the waveguide 1 as far asthe clamp 5 will allow. The single strip 2 is then doubled back onitself and loaded into the waveguide 1 so that the two parts of thestrip 2 lie one between each of the outer strips of the first group 3and the adjacent Waveguide wall. The loop in the single strip 2 shouldbe at the same end of the waveguide l as the bobbin 9 of the first group3.

The strips of the group 3 projecting from the opposite end of thewaveguide 1 are then divided into two equal groups and the ends of thestrips of the group 4 remote from the bobbin 10 are inserted in the gapso made. When the group 4 has been pushed as far as possible to wardsthe waveguide 1 by hand, the waveguide 1 is mounted on a hydraulicallyoperated drawn bench 13 and the mandrel is drawn into the waveguide 1 bya draw-bar 114 exerting a pullon a rod 15 passed through an axial holein the bobbin 9 of the first group of strips 3, in the J direction ofthe arrow. This pull is maintained until the mandrel substantially fillsthe waveguide 1 over the length which is to be bent.

To prevent the inner wall of the waveguide being scored by the edges ofthe strips during the loading operation, a hardened steel shoe 16 isarranged to abut the waveguide 1 at the opposite end to the drawbar 14so that the strips are aligned with one another prior to entering thewaveguide 1.

Two methods of actually forming the bend in the wtvegaide will now bedescribed, the foregoing description of the loading of the mandrel beingcommon to both these methods.

Referring now to FIGURE 2 of the drawings for the first method, thewaveguide 1, complete with the mandrel, is bent in a press tool whichcomprises a hydraulically operated ram 17 arranged to bear on one wallof the waveguide 1 and so to force the waveguide 1 to conform to theshape of a recess 18 formed in the corresponding part 19 of the presstool. In FIGURE 2 one half of the part 19 has been removed so that therecess 13 may clearly be seen. The ram 17 is triangular in shape, thepressure being applied to the base 20 of the triangle in the directionof the arrow, and the opposite apex 21 corresponding to the requiredcurvature of the wall of the waveguide 1 which is to be on the inside ofthe bend. The recess 18 is also triangular, the apex 22 of this trianglecorresponding to the required curvature of the wall of the waveguide 1which is to be on the outside of the bend. On completion of the pressstroke of the ram 17, which should be continuous, the waveguide 1 willbe constrained between the sides and bottom of the recess 18 and thelower surface of the ram 17.

In order to avoid corrugation of the wall of the waveguide 1 on whichthe ram 17 bears one or two strips 23 of metal similar to the stripsmaking up the mandrel may be interposed between the ram 17 and thewaveguide 1. There will naturally be some degree of spring-back of thewaveguide 1 when the pressure of the ram 17 is released and during thesubsequent operations. It is therefore necessary to bend the waveguide 1slightly more at this stage than is required in the final product, theamount of extra bending required being small and being found by trial.

After bending, the waveguide '1 is removed from the press tool and themandrel is removed on the draw bench shown in FIGURE 1 of the drawings.This is done by pulling the first group of strips 3 out of the waveguide1, in the same direction as that in which the mandrel was pulled in,until the bulk of the group of strips 3 has passed through thewaveguide 1. The single strip 2 and Lhe second group of strips 4 maythen be removed by and.

If necessary the waveguide 1 is then deburred and it is degreased priorto stress relieving in an air circulating furnace for a period of onehour at 250 C. to 270 C. After removal from the furnace the waveguide 1is allowed to cool in air.

When the waveguide 1 has been stress relieved, it is returned to thepress tool shown in FIGURE 2 of the drawings and the ram 17 is locked inits closed position by means of an eccentric cam lever operating in thehole 24 in the ram 17. The Waveguide 1 is then finally sized by forcingthrough it a series of highly polished hardened steel rollers, tallowagain being used as a lubricant. The rollers are fed through thewaveguide 1 by inserting them in sequence at one end and urging themthrough the waveguide 1 by means of pressure exerted on the mostrecently inserted roller. The first roller of the series, which ishereinafter referred to as the first working roller, is some twothousandths of an inch smaller than the required internal cross-sectionof the waveguide 1 on each dimension, this is followed by four rollershereinafter referred to as slave rollers, which are slightly smallerthan the first working roller and there follows in sequence a secondworking roller which is half a thousandth of an inch larger than thefirst working roller on each dimension, four slave rollers, a thirdworking roller, etc. until the fifth working roller which conforms tothe required internal cross-section of the waveguide 1.

The waveguide "1 is then removed from the press tool, is dcgreased andfinally bright acid dipped.

In the second method to be described it is required to provide thewaveguide 1 with two adjacent bends in the sarne plane, the two ends ofthe waveguide 1 being parallel or approximately parallel to one anotherwhen the two bends are completed, so that the finished shape of thewaveguide 1 approximates to a letter S, the type of mandrel which hasbeen previously described is again used.

in such a case the waveguide is bent in a jig instead of the press toolpreviously described. Referring to FIG- URE 3 of the drawing, the jigcomprises a first shoe 25 rigidly mounted on a base plate 26, one faceof the shoe 25 having a. recess 27 the dimensions of which correspond tothe dimensions of the waveguide 1. With one end of the waveguide 1 inposition in the recess 27, the open side of the recess 27 is closed by aclamping member 28 so that the waveguide 1 is rigidly held in place. Theother end of the waveguide 1 is clamped in a second shoe 2 which issimilar to the shoe 25 and which includes a recess 3% One end of athreaded shaft 31, which engages with an internally threaded member 32rigidly attached to the base plate 26, bears on one side of a plate 33on which the shoe 29' is mounted. Rotation of the shaft 31 causes theplate 33 and, therefore, the shoe 29 to be urged in a direction at rightangles to the longitudinal axis of the waveguide 1. The direction ofthis movement is controlled by projections 34 on the underside of theplate 33,

the projections 34 being free to slide in slots 35 in the baseplate 26.

The shoe 29 is mounted on the plate 33 by means of a projection 36 onthe underside of the shoe 29, the projection 36 being free to slide in agroove 37 formed in the plate 33, so that, as the plate 33 is urgedforward by the shaft 31, the shoe 29 is free to slide in a directionparallel to the longitudinal axis of the waveguide 1 in order to allowfor the fact that as the waveguide 1 is bent it will also beforeshortened. At the adjacent ends of the shoes 25 and 29 the recesses27 and 30 respectively are curved to correspond to the required finalcurvature of the waveguide 1 with the previously mentioned allowance forspring-back.

With the exception of this step, the manufacture of the waveguide 1 withtwo bends is the same as the first method described.

It will be realised that the invention is equally applicable towaveguides formed of other metals, for example, aluminum, and that itmay be used for a wide range of waveguide sizes and shapes of bend.

I claim:

1. A waveguide-bending mandrel comprising a stack of substantially flatelongated resilient metal strips, said stack including first and secondgroups of strips, each said group being longitudinally doubled back onitself and including means slidable on the strips for holding the stripstogether adjacent the loop so formed, the first and second groups ofstrips, when brought together to form the mans drel, being arranged withtheir respective loops at opposite ends of the mandrel and with all thestrips of the second group lying between two adjacent strips of thefirst group at least over that part of the length of the mandrel which,when it is in use, is to be within that part of the waveguide which isto be bent, the cross-section of at least said part of the length of themandrel being such that it is a close fit in the waveguide.

2. A waveguide-bending mandrel according to claim 1 wherein said metalis steel.

3. A waveguide-bending mandrel according to claim 1 wherein at leastsaid part of the length of the mandrel is References Cited in the fileof this patent of rectangular cross-secti0n. 4

4. A waveguide-bending mandrel according to claim 3 UNITED STATHOPATENTS including tWO additional strips similar to the strips form- 2- Wg t M 11 7, 1 111g said first and second groups of strips, saidadditional 5 3,324,945 rflih EC- 1 1 1 strips being arranged, when themandrel is in use, to lie 1,554,697 u ll r t a1- Jan. 3, 1928 onebetween each of the outer strips of said first group of 2,117,724IbbeiSOIl al y 17, 1938 strips and the adjacent wall of the waveguide.2,390,274 Rose et a1. Dec. 4, 1945 5. A waveguide-bending mandrelaccording to claim 4 2,672,224 Horwitz Mar. 16, 1954 wherein saidadditional strips are the two parts of a single 10 2,825,386 Fuchs Mar.4, 1958 strip doubled back on itself. 2,882,951 Fuchs et a1. Apr. 21,1959

